In conventional multiphase flow-metering, gas and liquid phases in a pipeline are separated in test separators. However, test separators are too expensive to install on a one per well basis. One test separator is usually installed at each production station and each well is produced over the separator when it is felt that a measurement of the well flowrate is essential. In practice this means that the flow from each well is only measured once per month and then only for a period of just one day. Test separators also suffer from a range of problems: they can be difficult to control, turndown is limited, they are bulky and can be non-representative because they only sample the flowrate for part of the production time of a well. For marginal fields, the cost of such separators can even make the development uneconomical so they are left out and the actual well flowrates are not measured.